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DEPARTMENT OF COMMERCE 

^; '■■ BUREAU OF FISHERIES 

Economic Circular No. 21 ::::::::: Issued October 14, 1916 

INFORMATION CONCERNING PARASITIC WORMS IN FISH. 

Health authorities in our coast cities from time to time have had 
their attention called to the presence of parasitic worms in fish. To 
dispel a reasonable doubt which arises in the minds of consumers and 
of health officers regarding the propriety of using as food the fish 
which harbor such parasites, the Bureau of Fisheries deems it proper 
to give publication to two statements which were prepared as a 
sequel to certain complaints filed with the Department of Health of 
New York City. The statements were prepared in response to re- 
quests from officers of that department. The first is by a special in- 
vestigator, who, in the service of the Bureau of Fisheries, has had an 
exceptionally wide experience in the study of the parasites of fishes, 
having examined many thousands of specimens of many species dur- 
ing a long period of years. The second is by an officer of the United 
States Bureau of the Public Health Service, who speaks from a broad 
knowledge of problems of public health, as well as from a vast ex- 
perience in the field of parasitology. 

STATEMENT BY PROF. EDWIN LINTON, SPECIAL INVESTIGATOR OF THE 
BUREAU OF FISHERIES. 

1. The public should know that in the order of nature there is a 
large number of species of animals and plants which pass all or a 
large part of their lives within other animals. Such forms are 
known as parasites. 

2. No species of animal is free from parasites, and probably no 
individual animal is for long free from parasites. 

3. Some parasitic forms, as the so-called trichinae of pork, will 
develop also in man. Hence the great danger of eating pork and 
other flesh that has not been thoroughly cooked. 

4. The flesh of most species of marine food fish is notal)ly free 
from parasites. 

5. Complaint has been made to the New York Health Department 
concerning the butterfish. An inquiry into the matter has shown 
that the parasites complained of are roundworm, or threarlworm, 
which, it was asserted, were found in the flesh. Very careful obser- 
vations made under the direction of the United States Bureau of 
Fisheries justifies the following explanation of the supposed occur- 

I 63308°— 16 






rence of roundworms, or threadworms (technically called nematodes) 
in the flesh of the butterfish. 

(a) Such worms are of frequent occurrence on the stomach and 
appendages of the stomach of the butterfish and of most fishes. 

(b) Careful examination of a large number of butterfish, carried 
on through a number of years and extending through many months 
of each year, I'csulted in the finding of only four threadworms in 
the flesh, one in each of four fishes out of ai)proximately 6,000 but- 
terfish examined. 

(c) Since threadworms are not uncommon on the stomach and 
stomach appendages of the butterfish, and sometimes are present 
in considerable numbers, persons who undertake to clean fish them- 
selves instead of having the retailer clean the fish for them, not dis- 
tinguishing between threadworms on the stomach appendages and 
threadworms in the flesh, on account of a misapprehension of the 
facts, may be tempted to throw perfectly good and wholesome food 
away and blame, most unjustly, the market for furnishing wormy 
fish.' 

(). Emi)hasis must be laid on the radial difference between such 
cases as that furnished by butterfish that have been made the basis 
of complaint, and meat in which insect larvse are developing. Un- 
fortunately, owing to the limitations of popular speech, both might be 
called " wormy." In the case of the parasitic worms, their presence, 
still active, would be an indication that the fish is comparatively 
fresh. In the case of insect larvae (maggots), no one needs to be told 
that their presence is very far from furnishing a guarantee that the 
flesh in which they are found is fresh. 

7. There is no reason to believe that any of the parasites of the 
butterfish. or indeed, of any of our marine food fishes, can develop in 
any of their stages of existence in man. Of course it should by now 
be well understood that all danger from infection by practically all 
parasites that occur in food is completely removed by thorough 
cooking. 

STATEMENT REGARDING THE NEMATODES OF BUTTERFISH, BY DR. C. W. 
STILES, bUREAU OF THE PUBLIC HEALTH SERVICE. 

There is no ground for uneasiness in the public mind because of 
the presence of small threadlike nematode parasites in butterfish 
offered for sale as food. 

These or very similar parasites are found in many different kinds 
of fishes, but no case is known in which they have caused disease in 
man nor is there any proof that tliey can do\elop in man. 

Usually the parasites are encysted among the entrails of the fish, 
so that when the fish are cleaned the parasites are removed. In some 



instances the nematodes are found in the flesh of the fish, but when 
the fish are cooked the parasites will be killed. 

There is no case known in which these parasites have been found 
alive in man, nor is any case known in which a person has been ren- 
dered ill from swallowing these nematodes in cooked or uncooked 
fish. 

Accordingly, so far as danger of disease is concerned, there is 
no necessity or justification for a food inspector to condemn fish 
because of the presence of the little nematodes. 

If fish are so heavily infested with the parasites as materially to 
alter the condition of the flesh and thus render it of less value or 
repellant to the consumer, a food inspector would be justified in con- 
demnation only from a business or an aesthetic point of view. But 
if a purchaser desired to purchase fish in this condition, for his 
own consumption and not for sale, with full knowledge of the inferior 
quality of said fish, there is no sound public health reason why he 
should not be permitted to do so. 

If the view were adopted that butterfish were to be condemned 
on public health grounds, solely because they contained these para- 
sites, consistency would call for the condemnation of all fishes, fowls, 
game, beef, mutton, pork, etc., for no food animal is known that does 
not contain some kind of parasite. A course of this kind would pro- 
duce much harm and no good, and could not be supported by known 
facts. 

The condemnation of food involves a destruction of property and 
should be based upon practical as well as theoretical considerations. 



WAf?HINGTON : GOVERNMENT PRINTINC, OFFICE : 1916 



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